1. Field of the Invention
The present invention relates to structure and method for constructing a circuit module suitable for hand-held electronic equipment with a slim body, e.g., a personal computer that is required to mount electronic elements in a high density in the body. In particular, the present invention relates to structure and method for constructing a circuit module having a novel radiating mechanism that can achieve sufficient radiating efficiency while maintaining reliability of the circuit module during long-term usage.
2. Discussion of the Related Art
Typically, handheld electronic equipment with a slim body, such as a note-book type or a mobile type personal computer (PC), are required to install electronic elements including heating source elements, such as IC chips, in a high density in the slim body. With the widespread use and diversification in the handheld electronic equipment, in particular, in personal computers, there is a strong demand for increasing applications to enhance functions and raise performance of the personal computer.
To enhance functions and raise performance of a personal computer with a slim and small body, there is a need to increase packaging density of electronic elements including heating source elements, such as IC chips, in the slim body. It is also required to increase the number of the electronic elements packaged in order to enhance the functions and to achieve higher performance of the computer.
To enhance the functions of the personal computer, it is substantially required to increase the packaged number of heating source electronic elements, i.e., semiconductor chips, such as IC chips. Consequently, the total amount of the heat generated from the heating source electronic elements rapidly increases in the slim body. To avoid the generated heat adversely affecting other electronic elements installed in the body, the heat in the body need to be sufficiently radiated.
Conventionally, a heat sink unit is commonly used as a radiating mechanism for the generated heat from IC chips in the body of the personal computer. Usually, the heat sink unit is made of a high heat conductivity material, such as aluminum. The heat sink unit includes a radiation panel and a plurality of radiating projections. The radiation panel of the heat sink unit is connected to the heating source element, e.g., an IC chip, in order to transfer and radiate the heat generated from the IC chip into the air through the radiation projections. To increase efficiency of the radiation, it has been considered to increase the radiating surfaces of the heat sink unit as large as possible.
Typically, the circuit module installed in the personal computer includes various components mounted on a printed wire board. Thus, the circuit module is constructed by mounting, for example, a heat sourcing IC, a semiconductor package and a heat sink unit on a printed wire board. However, when the various components are constructed as the circuit module, generally various dimensional tolerances are generated due to the design errors among these components.
Recently, to enhance the packaging density and to achieve multi-connecting pins of the semiconductor package, a Ball Grid Array (BGA) package is widely used as a semiconductor package for installing components in the circuit module. The BGA package is usually connected to a base plate of the printed circuit board through a plurality of ball type solders. However, in the circuit module using the BGA package, there may appear dimensional tolerances during the construction of the circuit module due to deformations of the plurality of ball solders.
If the dimensional tolerance exceeds a permissible positive absolute amount during the construction of the circuit module, a spacing gap is produced in the connecting surfaces between the IC chip and the radiating panel of the heat sink unit. Such a spacing gap deteriorates the efficiency of the radiation through the heat sink unit.
Further, if the dimensional tolerance exceeds a permissible negative absolute amount during the construction of the circuit module, overload stresses appear at the connecting portions with each of the elements since each element presses against others. The stresses at the connecting portions deteriorate reliability of the circuit module for long-term usage.
To avoid the influences of stress, it has conventionally been proposed to interpose a heat connecting material, such as a cool sheet or a grease, between the IC chip and the heat sink unit in order to absorb the dimensional tolerances of elements. Further, it has been proposed to provide a spring mechanism between the printed wire board and the heat sink unit.
However, each of the conventional proposals has serious defects for applying to the circuit module for installing in the personal computer.
Thus, if a cool sheet is interposed between a IC chip and a heat sink unit, the efficiency of the radiation of the generated heat in the circuit module deteriorates depending upon the thickness of the cool sheet since the heat resistance of the cool sheet increases depending upon its thickness. Moreover, when the dimensional tolerances among the elements approaches the maximum amount, it is impossible for the disposed cool sheet to absorb the squeezing power generated between the elements. Consequently, stresses due to the squeezing power concentrate at the connecting portions of the elements. As explained above, this causes deterioration of the reliability of the circuit module.
By providing grease between an IC chip and a heat sink unit, it is possible to reduce the stresses at the connecting portions of the elements. However, the grease leaks around the IC chip deteriorating the efficiency of the radiation.
To absorb the stresses generated at the connecting portions of the module elements, it has been proposed to dispose a spring at the attaching portion between the printed wire board and the heat sink unit. However, such a conventional coupling between the printed wire board and the heat sink unit through the spring requires a very complicated structure for mounting the circuit module.
Furthermore, it has conventionally been proposed to provide metal wires between a heating source element and a radiation unit for transferring the generated heat to the radiation unit. Each of the metal wires has a thermal conductivity and flexibility. It is possible to absorb the dimensional tolerance by using the metal wires. However, the metal wires have a serious defect for obtaining a sufficiency of the radiation effect since the metal wires have small contacting surfaces to the heating element and the radiator.
As explained above, it is essential for a circuit module applicable to a personal computer with a high density to solve both of the reduction of the stresses due to the dimensional tolerances among the circuit elements and the efficient transfer of the heat emitted from the exothermic electronic element, e.g., the IC chip, to the radiation unit. However, there is no teaching of the circuit module that can achieve both the absorption of the dimensional tolerances and the high efficiency of the heat transferring effect of the heat emitted from the IC chip.
Accordingly, the present inventions is directed to apparatus and method that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the apparatus and method particularly pointed out in the written description and claims hereof as well as the appended drawings.
In accordance with the present invention, there is provided a circuit module structure comprising a wiring base board provided with a wiring pattern, an electronic element mounted on the wiring base board, and a heat sink unit fixed on the wiring board for radiating heat emitted from the electronic element. The heat sink unit includes a radiation panel facing toward the electronic element and having a heat conductivity. Also provided is a heat conducting element between a surface of the heat sink unit facing the electronic element. The heat conducting element comprises a plurality of thin plate-like members having a heat conductivity substantially the same as that of the radiation panel and for transferring the heat emitted from the surface of the electronic element to the radiation panel and a predetermined flexibility for absorbing stresses generated due to dimensional tolerances of the electronic element.
Also in accordance with the present invention, there is provided handheld electronic equipment comprising a slim main body for attaching a data inputting device on one surface of the body and a circuit module provided under the data inputting device in the main body. The circuit module includes a base board provided with a wiring pattern, an IC chip mounted on the base board, and a heat sink unit fixed on the base board. The heat sink unit includes a radiation panel facing toward the IC chip and a heat conducting element provided between the IC chip and the radiation panel of the heat sink unit. The heat conducting element includes a plurality of thin plates each having a heat conductivity for transferring heat emitted from the IC chip to the heat sink unit and a predetermined flexibility for preventing stress from being applied to the IC chip.
Further, in accordance with the present invention, there is provided electronic equipment, comprising: a main body for housing a circuit module, the circuit module having a plurality of circuits for working the electronic equipment, the circuit module including: a base board provided with a wiring pattern; an IC chip mounted on the base board; and a heat sink unit fixed on the base board, the heat sink unit including a radiation panel facing toward the IC chip and a heat conducting element provided between the IC chip and the radiation panel of the heat sink unit, the heat conducting element including a plurality of thin plates each having a heat conductivity for transferring h eat emitted from the IC chip to the heat sink unit and a predetermined flexibility for preventing stress from being applied to the IC chip.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.